Is a world population of 6 billion too many? Compare that with animals. There are more than a million animal species. There are 6,000 species of reptiles, 73,000 kinds of spiders, and 3,000 types of lice. For each person there is about 200 million insects. The 4,600 kinds of mammals represent a mere 0,3% of animals and the 9000 kinds of birds only 0,7%. The most numerous bird specie is the red-billed quelea of southern Africa. There are an estimated 100 trillion of them.